This invention relates generally to a method and apparatus for controlling a robot hand along a predetermined path. More particularly, the invention relates to a method and apparatus for controlling a robot hand, which is suitable for use in improving the accuracy with which the robot hand moves along the predetermined path and at a predetermined speed, and effectively applicable to the control of the robot having a plurality of axes of motion which determine a position and orientation of the robot hand.
Recently, the robots have been more and more introduced to various industrial fields for automating work or promoting labor welfare. This wide application of the robots creates needs for controlling the robot hand precisely along the predetermined path at the predetermined speed. An interpolating method is known as one of the effective control techniques for precisely moving the robot hand, which interpolates the path of the robot hand between teaching points.
Methods of interpolating the path of the robot hand include a method based on position-controlling operations and a method based on speed-controlling operations. In the method based on position-controlling operations, actual position data obtained by subjecting an actual pair displacement which indicates the actual position of the robot hand to coordinate conversion, and target position data are used to compute a target position for a subsequent sampling operation. The actual pair displacement is subtracted from a target pair displacement obtained by subjecting the target position to coordinate conversion, and the resultant value is multiplied by k to determine an instruction pair displacement, the target value, for each rotary pair, and these instruction pair displacements are input to a driving system. The driving system is provided with the same number of driving circuits of the same construction as the number of degrees of freedom of the robot hand.
On the other hand, the method based on speed controlling operations is carried out as follows. Namely, when an instruction for moving a robot hand from its present position to a target position is given, a target speed for a subsequent sampling operation is computed on the basis of the actual position data and the target position data, and the target speed is subjected to coordinate conversion to determine a pair speed for each rotary pair, and these pair speeds are input to a driving system.
In the method of interpolating the path of a robot hand which is based on speed-controlling operations, one of the conventional methods, a speed curve with respect to a predetermined path is established in advance, and the target position for the subsequent sampling operation is determined by using the speed curve. However, the speed of the robot hand deviates constantly from a re-set speed curve, since it varies with load. Consequently, the robot hand moves off the path, or the speed of the robot hand varies to prevent the robot hand moving at a constant speed. Once the robot hand has moved off the path, it is impossible to return it thereto. This means that it is difficult to move the robot hand correctly along the path.
Another path-interpolating method has been developed with a view to eliminating the drawbacks encountered in the above methods. In this method, the deviation of the robot hand from a pre-set path is computed, and the value of a controlling speed proportional to the resultant deviation is added to a command speed value to improve the accuracy with which the robot hand moves along the pre-set path. However, this method of interpolating the path of a robot hand cannot improve to a fully satisfactory extent the accuracy with which the robot hand moves along the pre-set path.